GIANT MAGNETORESISTANCE STUDIES ON LA-(0.8-X)R(X)SR(0.2)MNO(3) THIN-FILMS (R=PR,ND,GD,HO)

The effect of substituting La by a smaller lanthanide element (R) in L a(0.8-x)R(x)Sr(0.2)MnO(3) (x = 0.1; R = Pr, Nd, Gd, Ho) thin films on the resistivity (rho) and giant magnetoresistance (GMR) behaviour was studied. The magnitude of GMR shows a maximum as a function of tempera ture. The temperature at which the maximum value of GMR is observed wa s found to shift systematically towards higher temperatures (from 210 to 300 K) as the size of the substitution ion increases from Ho to Pr, rho(T) also shows a maximum which shifts to higher temperatures as th e size of the substitution ion increases. The zero-field resistivity s hows a systematic decrease as the size of R(3+) increases. This result is explained qualitatively by invoking the interrelation between the conduction electron hopping probability and the Mn-O-Mn bond angle dis tortion which, in turn, is governed by the size of the substitution io n. Our results show that the size of the rare earth substitution ion c an play an important role in tailoring the resistivity and GMR behavio ur of La-R-Sr-Mn-O thin films, particularly for room temperature appli cations.